A compound having an optically active dihydrobenzofuran ring (e.g., [(3S)-6-({2′,6′-dimethyl-4′-[3-(methylsulfonyl)propoxy]biphenyl-3-yl}methoxy)-2,3-dihydro-1-benzofuran-3-yl]acetic acid) as a GPR40 receptor agonist useful as a drug for the prophylaxis or treatment of diabetes and the like, and a production method thereof (WO2008/001931).